1. Field of the Invention
The present invention relates to a wheel support bearing assembly for rotatably supporting a vehicle wheel that serves as a vehicle drive wheel used in, for example, automotive vehicles and also to a crimping method therefor.
2. Description of the Prior Art
The wheel support bearing assembly for rotatably supporting a vehicle drive wheel of a structure shown in FIGS. 23 and 24 has been well known in the art. The wheel support bearing assembly shown in FIGS. 23 and 24 is disclosed in, for example, the Japanese Laid-open Patent Publication No. 9-164803, laid open to public inspection on Jun. 24, 1997. Referring to FIGS. 23 and 24, the known wheel support bearing assembly includes double rows of balls 25 operatively interposed between raceways 23 defined in an outer member 21 and raceways 24 defined in an inner member 22, respectively. The inner member 22 is made up of a hub axle 29 having an outer periphery formed with a radially outwardly extending hub flange 29a for the support of the vehicle wheel and an inner race segment 30 mounted externally on a portion of the outer periphery of the hub axle 29 on an inboard side.
The hub axle 29 has an axial bore 31 defined therein, to which a stem portion 33a of an outer race 33 of the constant velocity joint is splined. With the stem portion 33a splined to the hub axle 29 in this manner, an annular shoulder 33b of the stem portion 33a of the outer race 33 of the constant velocity joint is urged against an inboard end face 30a of the inner race segment 30. When a nut 34 is threaded onto an externally threaded free end of the stem portion 33a while the annular shoulder of the stem portion 33a is held in abutment with the inner race segment 30, the inner race segment 22 can be fastened axially by and between the outer race 33 of the constant velocity joint and the nut 34.
In the known wheel support bearing assembly of the structure discussed above, the inner race segment 30 is mounted on a radially inwardly depressed inner race mount 35 defined in an outer periphery of an inboard end portion of the hub axle 29 and, on the other hand, an inboard inner peripheral edge portion of the inner race segment 30, that is delimited between an annular inboard end face thereof and an inner peripheral surface thereof, is depleted axially inwardly of the inner race segment 30 to define a counterbore 36, with the inboard end of the hub axle 29 crimped radially outwardly to allow it to be nested within the counterbore 36. In which way, an undesirable separation of the inner race segment 30 from the hub axle 29, which would otherwise occur under the influence of an external force generated during the mounting of the wheel support bearing assembly on the vehicle body structure, is prevented.
However, this known wheel support bearing assembly has been found having the following problems:                (1) Since a crimped portion 29b of the hub axle 29 is large in size, the radial size of the counterbore 36 formed in the inboard end of the inner race segment 30 must necessarily be within the range of 5 mm to 7 mm in terms of the difference in diameter between the inner peripheral surface of the inner race segment 30 and the diameter of the counterbore 36. If the radial size of the counterbore 36 is so large as described above, the surface area of the inboard end face 30a of the inner race segment 30 decreases correspondingly and, therefore, the pressure of contact with the shoulder 33b of the outer race 33 of the constant velocity joint increases. This leads to a cause of generation of frictional wear and/or obnoxious noises.        (2) When an attempt is made to allow the crimped portion 29b of the hub axle 29 to be accommodated inside of the inboard end of the inner race segment 30, the axial length of the counterbore 36 in the inner race segment 30 must necessarily be within the range of 7 mm to 8 mm. The increased axial length of the counterbore 36 in the inner race segment 30 causes the counterbore 36 in the inner race segment 30 to be positioned on the imaginary line drawn to define the ball contact angle and, therefore, there is the possibility that the inner race segment 30 may be deformed considerably under the influence of an applied load during the operation to such an extent as to reduce the life of the wheel support bearing assembly.        
The increased axial length of the counterbore 36 may also result in reduction of the mounting length (surface area), over which the inner race segment 30 is mounted on the hub axle 29, and, accordingly, creepage of the inner race segment 30 is apt to occur, accompanied possibly by reduction of the bearing life. Although those problems can be resolved if the inner race segment having an increased axial length is employed, the use of the inner race segment of the increased axial length in turn require an extra space in a direction axially thereof.                (3) Also, since the crimped portion 29b of the hub axle 29 is large in size, a crimping tool will interfere with the inner race segment 30 during the practice of a vibratory crimping process, making it difficult to accomplish the crimping.        